1. Field of the Invention
This invention generally relates to magnetic sensors and transducers that read information and signals recorded on magnetic recording media, and particularly to magnetoresistive heads whose operations depend on magnetoresistive effects. In addition, this invention also relates to magnetic resistance detection systems and magnetic storage systems, which are equipped with the magnetoresistive heads.
This application is based on Patent Application No. Hei 11-171661 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
Conventionally, there are provided a variety of magnetic reading heads (or transducers), which are called magnetoresistive (MR) sensors or heads. It is well known that those sensors or heads are capable of reading data on magnetic surfaces of media with great linear densities. Generally speaking, the MR sensors detect magnetic-field signals by using resistance variations, which represent functions regarding intensities and directions of magnetic fluxes being sensed by reading elements. The conventional MR sensor operates based on the anisotropic magnetoresistive (AMR) effect in which one component of resistance of a reading element varies in proportion to the square of the cosine of an angle being formed by a magnetization direction and a direction of a sensing current flowing in the reading element. Detailed explanations for the AMR effects are written on various papers such as the paper entitled xe2x80x9cThin Film Magnetoresistors in Memory, Storage and Related Applicationsxe2x80x9d written by Dr. David A. Thompson and his members and published by IEEE Trans.on Mag. MAG-11, p.1039 on 1975, for example. Generally, the magnetic heads using the AMR effects frequently apply longitudinal bias to reduce Barkhausen noise. In some cases, antiferromagnetic materials such as FeMn, NiMn and nickel oxide are used as materials for application of longitudinal bias.
Recently, several papers report remarkably enhanced magnetoresistive effects, in which resistance variations of laminated magnetic sensors bring spin-dependent transmission of conduction electrons between magnetic layers sandwiching a non-magnetic layer as well as spin-dependent scattering of conduction electrons on accompanying interfaces. Those effects are called by various names such as xe2x80x9cgiant magnetoresistive effectsxe2x80x9d or xe2x80x9cspin-bubble effectsxe2x80x9d. The magnetoresistive sensors using those effects are made by materials, which are adequately selected. As compared with the general sensors using the AMR effects, those sensors are greatly improved in sensitivity and are accompanied with great variations of resistance. In those magnetoresistive sensors, plane resistance being measured between a pair of ferromagnetic layers, which are separated from each other by a non-magnetic layer, varies in proportion to the cosine of an angle being formed between magnetization directions of the two ferromagnetic layers.
Japanese Unexamined Patent Publication No. Hei 2-61572 (i.e., Japanese Patent No. 2,651,015) discloses a laminated magnetic structure that brings high magnetoresistive variations being caused by anti-parallel alignment of magnetized elements in magnetic layers. As materials applicable to the laminated magnetic structure, the specification of the above patent publication lists transition metals and alloys. It also teaches a structure additionally incorporating a fixing layer, which is fixed to at least one of two ferromagnetic layers being separated by an intermediate layer. In addition, it teaches that a material of FeMn is appropriate for formation of the fixing layer.
Japanese Unexamined Patent Publication No. Hei 4-103014 discloses a ferromagnetic tunnel junction element using multilayer films in which an intermediate layer is inserted into ferromagnetic layers. Herein, it teaches a ferromagnetic tunnel effect film in which bias magnetic field is applied to at least one ferromagnetic layer by an antiferromagnetic substance.
In general, magnetoresistive effect elements of a shield type using ferromagnetic tunnel junction (MTJ) films employ a basic configuration made by three layers, i.e., a free layer, a barrier layer and a fixing layer. Herein, the barrier layer is an insulation layer, while the free layer and fixing layer are metal layers. Such a basic configuration of the free layer, barrier layer and fixing layer substantially acts like a capacitor, so there is a drawback in that electric charges are easily accumulated in the free layer and fixing layer. In other words, electric charges are accumulated in areas between the free layer and fixing layer in a manufacturing process of the magnetoresistive effect element. If a great amount of electric charges are accumulated between them, large voltages are likely applied to both end surfaces of the barrier layer. So, the barrier layer is likely destructed by electric discharge. Resistance variations of the magnetoresistive effect element using the MTJ film are caused by polarization of ferromagnetic substances at both ends of the insulation layer. If insulating destruction is caused so that an electric current bypass is being formed, the magnetoresistive effect element does not produce resistance variations any more.
A magnetic recording/reproduction head using an MTJ film is manufactured by prescribed steps, an outline of which is as follows:
(1) Shield formation.
(2) Lower gap formation.
(3) Lower electrode formation.
(4) MTJ film formation.
(5) Longitudinal bias formation.
(6) Upper electrode formation.
(7) Upper gap formation.
(8) Common pole formation.
(9) Yoke formation.
(10) Coil formation.
(11) Insulator formation.
(12) Upper pole formation.
(13) Terminal formation.
(14) ABS plane lapping.
In the above, photoresist (PR) formation techniques are frequently used for formation of the lower shield, lower gap, lower electrode, MTJ film, longitudinal bias, upper electrode, upper gap, common pole, yoke, coil, insulator and upper pole. Herein, baking operations are performed, such as pre-baking, positive/negative inversion baking and post-baking with regard to photoresists. Those operations are performed in the high-temperature and dry atmosphere, in which static electricity is easily caused to occur. Occurrence of the static electricity after the MTJ film formation causes immediate electrostatic destruction of the barrier layer. In some of the aforementioned steps, milling is performed after formation of the photoresist. However, the milling causes generation of ions, which charge up the (MTJ) free layer and fixing layer. This sometimes causes electrostatic destruction of the barrier layer.
As described above, the barrier layer of the MTJ film is likely destructed by electric charges being caused during manufacturing operations. As a result, the aforementioned manufacturing technique cannot produce magnetoresistive heads well, so there is a problem in that yield in manufacture of magnetoresistive heads is greatly reduced.
It is an object of the invention to provide a magnetoresistive head that is designed to avoid electrostatic destruction thereof in manufacture.
It is another object of the invention to provide a magnetic resistance detection system and a magnetic storage system, each of which is equipped with the magnetoresistive head.
A magnetoresistive head whose operation depends on a magnetoresistive effect is configured using a ferromagnetic tunnel junction (MTJ) film, which is arranged between a lower electrode and an upper electrode. The ferromagnetic tunnel junction film is basically configured using a set of a free layer, a barrier layer and a fixing layer, which are sequentially formed and laminated on the lower electrode. Longitudinal bias layers and insulation layers are arranged on both sides of the ferromagnetic tunnel junction film.
This invention is characterized by that the ferromagnetic tunnel junction film is designed to avoid electrostatic destruction in manufacture by prescribed measures. For example, the barrier layer is reduced in thickness at a terminal portion as compared with a center portion. Or, the barrier layer has a defect at the terminal portion. In addition, it is possible to provide a conductor in connection with the barrier layer in proximity to its terminal portion. Further, it is possible to attach re-adhesive substance, which is produced by milling for patterning of the ferromagnetic tunnel junction film, to a specific terminal surface of the ferromagnetic tunnel junction film which is opposite to an ABS plane. Those measures provide a bypass allowing overcurrent release between the free layer and fixing layer. Moreover, adjustment milling or plasma oxidation is employed to control an amount of the re-adhesive substance being attached to the terminal surface of the ferromagnetic tunnel junction film. Thus, by adequately optimizing the amount of the re-adhesive substance, it is possible to improve yield in manufacturing the magnetoresistive heads.
In addition, it is possible to propose a magnetic resistance detection system and a magnetic storage system using the aforementioned magnetoresistive head. For example, a magnetic disk device installs magnetic disks, on which data are recorded or reproduced by the magnetoresistive heads.